This invention relates generally to the field of gas turbine engines, and more particularly to a pre-mix burner for a gas turbine engine.
Gas (combustion) turbine engines are used for generating power in a variety of applications including land-based electrical power generating plants. Gas turbines may be designed to combust a broad range of hydrocarbon fuels, such as natural gas, kerosene, biomass gas, etc. Gas turbines are known to produce an exhaust stream containing a number of combustion products. Many of these byproducts of the combustion process are considered atmospheric pollutants, and increasingly stringent regulations have been imposed on the operation of gas turbine power plants in an effort to minimize the production of these gasses. Of particular concern is the regulation of the production of the various forms of nitrogen oxides collectively known as NOx. It is known that NOx emissions from a gas turbine increase significantly as the combustion temperature rises. One method of limiting the production of nitrogen oxides is the use of a lean mixture of fuel and combustion air, i.e. a relatively low fuel-to-air ratio, thereby limiting the peak combustion temperature to a degree that reduces the production of NOx. However, higher combustion temperatures are desirable to obtain higher efficiency and reduced production of carbon monoxide.
Two-stage combustion systems have been developed that provide efficient combustion and reduced NOx emissions. In a two-stage combustion system, diffusion combustion is performed at the first stage for obtaining ignition and flame stability. In diffusion combustion, the fuel and air are mixed together in the same chamber in which combustion occurs, i.e. the combustion chamber. Premixed combustion is performed at the second stage to reduce NOx emissions. In pre-mix combustion, the fuel and air are mixed together in a pre-mixer that is separate from and upstream of the combustion chamber. The first stage is referred to as the pilot stage, and it is a significant contributor to the overall amount of NOx emissions even though the percentage of fuel supplied to the pilot is comparatively small, often less than 10% of the total fuel supplied to the combustor.
It is further known to utilize a two-stage combustor wherein the pilot stage incorporates both a diffusion portion and a pre-mixed portion, as illustrated in U.S. Pat. No. 4,982,570 for example. The pre-mixer portion of such systems is easily damaged by flame flashback into the pre-mixing chamber that may occur during certain transient operating conditions.
Thus, a pre-mix burner that is resistant to the occurrence of flashback is desired. A burner for a gas turbine engine is described herein as including: a pre-mix chamber for directing a flow of air; a fuel peg extending into the flow of air, the flow of air past the fuel peg defining an upstream direction and a downstream direction; and a fuel outlet formed in the fuel peg for delivering a flow of fuel in a downstream direction transverse to the direction of the flow of air past the fuel peg. The fuel outlet may be formed to direct the flow of fuel at a 45xc2x0 angle plus or minus 15xc2x0 relative to a plane extending in a direction of a wake formed downstream of the fuel peg. The burner may include a plurality of fuel outlets formed along a length of the fuel peg, alternate ones of the fuel outlets being disposed at respective positive and negative angles relative to a plane extending in a direction of a wake formed downstream of the fuel peg.
A two-stage burner for a gas turbine engine is described herein as including: a diffusion burner; a structure disposed about the diffusion burner defining an annular pre-mixing chamber around the diffusion burner for the passage of a flow of air; a plurality of fuel pegs extending into the pre-mixing chamber; and a plurality of fuel outlet openings formed in each fuel peg, each fuel outlet opening directing a flow of fuel into the pre-mixing chamber in a generally downstream direction at an angle transverse to a direction of the flow of air past the respective fuel peg to direct the flow of fuel away from a wake formed in the flow of air downstream of the respective fuel peg. A majority of the fuel outlet openings of each peg may be formed within a center half of a cross-sectional dimension of the pre-mixing chamber, or all of the fuel outlet openings of each peg may be formed within a center two-thirds of a cross-sectional dimension of the pre-mixing chamber. Alternate ones of the plurality of fuel outlet openings may be disposed in a respective fuel peg at respective positive and negative angles relative to a plane extending in a direction of the wake. A gas turbine engine including such a two-stage burner is also described.